std::istream_iterator - cppreference.com (original) (raw)

| Defined in header | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | ------------- | | template< class T, class CharT = char, class Traits = std::char_traits<CharT>, class Distance = std::ptrdiff_t > class istream_iterator : public std::iterator<std::input_iterator_tag, T, Distance, const T*, const T&> | | (until C++17) | | template< class T, class CharT = char, class Traits = std::char_traits<CharT>, class Distance = std::ptrdiff_t > class istream_iterator; | | (since C++17) |

std::istream_iterator is a single-pass input iterator that reads successive objects of type T from the std::basic_istream object for which it was constructed, by calling the appropriate operator>>. The actual read operation is performed when the iterator is incremented, not when it is dereferenced. The first object is read when the iterator is constructed. Dereferencing only returns a copy of the most recently read object.

The default-constructed std::istream_iterator is known as the end-of-stream iterator. When a valid std::istream_iterator reaches the end of the underlying stream, it becomes equal to the end-of-stream iterator. Dereferencing or incrementing it further invokes undefined behavior. An end-of-stream iterator remains in the end-of-stream state even if the underlying stream changes state. Absent a reassignment, it cannot become a non-end-of-stream iterator anymore.

A typical implementation of std::istream_iterator holds two data members: a pointer to the associated std::basic_istream object and the most recently read value of type T.

T must meet the DefaultConstructible, CopyConstructible, and CopyAssignable requirements.

Contents

• 1 Member types
• 2 Member functions
• 3 Non-member functions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Member types

[edit] Member functions

[edit] Non-member functions

[edit] Notes

When reading characters, std::istream_iterator skips whitespace by default (unless disabled with std::noskipws or equivalent), while std::istreambuf_iterator does not. In addition, std::istreambuf_iterator is more efficient, since it avoids the overhead of constructing and destructing the sentry object once per character.

[edit] Example

#include #include #include #include #include   int main() { std::istringstream str("0.1 0.2 0.3 0.4"); std::partial_sum(std::istream_iterator(str), std::istream_iterator(), std::ostream_iterator(std::cout, " "));   std::istringstream str2("1 3 5 7 8 9 10"); auto it = std::find_if(std::istream_iterator(str2), std::istream_iterator(), [](int i){ return i % 2 == 0; });   if (it != std::istream_iterator()) std::cout << "\nThe first even number is " << *it << ".\n"; //" 9 10" left in the stream }

Output:

0.1 0.3 0.6 1 The first even number is 8.

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also